FIG. 1 depicts a portion of a conventional magnetic transducer 10, such as a conventional read transducer, as viewed from the air-bearing surface (ABS). The conventional transducer 10 includes a conventional bottom shield 12, a nonmagnetic underlayer 13, conventional NiFe seed layer 14, conventional nonmagnetic seed layer 16, conventional antiferromagnetic (AFM) layer 18, conventional sensor 20, conventional capping layer 36, and conventional top shield 40. The conventional shields 12 and 40 typically include NiFe and are formed by plating. The conventional underlayer 13 typically includes materials such as Ta, CoFeB, and NiFeB. The conventional nonmagnetic seed layer 16 is typically Ru or NiFeCr.
The conventional sensor 20 is in a current-perpendicular to plane (CPP) configuration. In a CPP configuration, read current is driven generally perpendicular to the plane of the layers of the device, along the z-axis shown. The sensor 20 typically includes a conventional pinned layer 24, a conventional nonmagnetic spacer layer 28, and a conventional reference layer 30. The conventional nonmagnetic spacer layer 28 is typically a tunneling barrier layer. The conventional free layer 34 has a magnetization that is substantially free to change direction in response to an applied magnetic field, for example from a bit being read. The conventional tunneling barrier layer 32 may allow conduction through the sensor 20 via tunneling. The sensor 20 is thus a tunneling magnetoresistive (TMR) sensor. Note that if a conductive spacer layer is used instead of the barrier layer 32, then the sensor 20 is a spin valve. The pinned layer 24 shown is a synthetic antiferromagnet (SAF) includes a first pinned layer 26, a nonmagnetic spacer 28, and a reference layer 30. The reference layer 30 and pinned layer 26 are typically antiferromagnetically coupled. The magnetization(s) of the conventional SAF layer 24 are pinned by the conventional AFM layer 18. More specifically, the pinned layer 26 typically has its magnetization pinned by the conventional AFM layer 18, for example via exchange interaction. The remaining ferromagnetic layer, or reference layer 30, has its magnetization pinned because it is strongly magnetically coupled with the pinned layer 26.
The conventional transducer 10 also includes a conventional NiFe seed layer 14. The NiFe seed layer 14 is approximately fifty percent Ni and fifty percent Fe (Ni0.5Fe0.5). The conventional Ni0.5Fe0.5 seed layer 14 is magnetic. Such a conventional Ni0.5Fe0.5 seed layer 14 improves the thermal stability of the AFM layer 18 grown on the conventional Ni0.5Fe0.5 seed layer 14. In particular, as the recording density increases, the distance between the shields 12 and 40 is reduced. The AFM layer 18 has a decreased volume. This decrease in volume may reduce the distribution of blocking temperatures (TbD). The lowering of the TbD reduces the thermal stability of the AFM layer 18 and, therefore, the stability of the SAF pinned layer 24. This would adversely affect performance of the conventional transducer 10. The conventional mechanism for addressing this is the use of the Ni0.5Fe0.5 seed layer 14. If the AFM layer 18 is grown on the conventional Ni0.5Fe0.5 seed layer 14, then the AFM layer 18 has a larger grain size, a higher anisotropic energy or both. Thus, the thermal stability of the read sensor 20 may be improved even at higher recording densities and smaller shield-to-shield spacing.
Although the conventional sensor 20 functions, there are drawbacks. For example, the conventional Ni0.5Fe0.5 seed layer 14 typically has a very large positive magnetostriction. The magnetostriction may adversely affect sensor 20 performance. For example, more noise may be generated. This magnetostriction may also induce an undesired magnetic anisotropy perpendicular to the ABS. The magnetic anisotropy of the Ni0.5Fe0.5 seed layer 14, which may be considered to be part of the shield 12, affects the shield 12. The conventional shield 12 may thus become unstable during recording or in the presence of external stray fields. In addition, the conventional Ni0.5Fe0.5 seed layer 14 may be overmilled at its sides. If this occurs, the relatively high magnetization of the conventional Ni0.5Fe0.5 seed layer 14 may weaken the effect of hard bias layer (not shown). As a result, the free layer response amplitude, asymmetry, and noise are adversely affected. Thus, the conventional read transducer 10 may not function as desired at higher recording densities.
Accordingly, what is needed is a system and method for providing a read transducer having improved performance at higher densities.